The present invention relates to a yarn winding apparatus of the type having a rotatable turret or revolver which mounts a pair of winding spindles, and wherein the spindles are serially delivered to a winding position and a doffing position as the revolver is sequentially rotated.
Winding machines of the above described type commonly employ a contact roll which is positioned to rest upon the package being formed on the spindle at the winding position. Also, designs are known wherein the revolver is rotated to provide relative movement between the contact roll and the winding spindle as the package diameter builds, note EP-B1 1359, U.S. Pat. No. 4,298,171 and EP-B 15410.
In such known winding machines, the contact roll is rigidly supported by the machine frame. The winding spindles are mounted on rocking arms, which are pivotally supported on the revolver, so that the winding spindles can occupy an outer and inner radial position relative to the revolver. At the beginning of a winding operation the relative movement between the winding spindle and contact roll, with the revolver at a standstill, is effected by pivoting the rocking arm. Subsequently, the rocking arm is secured relative to the revolver, and the relative movement between the winding spindle and the contact roll is effected by rotating the revolver. To this end, a torque is exerted on the revolver by means of pneumatic and hydraulic cylinders. This torque is counteracted by the torque of the force which is exerted by the stationary contact roll on the package or respectively the winding spindle. The increase of this force causes the revolver to rotate as the package diameter increases.
In the course of a winding cycle, unsteady changes of the radial force which exists between the contact roll and the package to be formed, occur on the winding machine. These result from the fact that the contact pressure is applied by the very same control devices which also control the relative movement between the contact roll and the operating winding spindle. Consequently, the stick-slip effects, which are unavoidable at the slow rotation of the revolver, result in fluctuations, and particularly in unsteady fluctuations, of the contact pressure.
U.S. Pat. No. 4,106,710 discloses a winding machine in which the revolver is stopped during a winding cycle, and thus the winding spindle in operation remains stationary. The contact roll is supported on a slide, which is movable substantially radially to this winding spindle. Consequently, the contact roll can perform a movement relative to the slide. As a function of this movement, pneumatic cylinder-piston assemblies are controlled which serve to compensate for the weight of the slide. Thus, the contact roll does not rest on the package with the weight of all structural parts of the slide, but only with a reduced force. As the package diameter increases, the package must therefore apply the force necessary to move the slide, which corresponds to the aforesaid reduced force.
DE-OS 25 44 773 discloses a winding machine in which the winding spindle is supported in a movable slide. The contact roll is supported in a likewise movable support. The slide of the winding spindle is held by pneumatic cylinders, which are biased by pressure as a function of the movement of the support of the contact roll, thereby compensating for the weight of the slide with the winding spindle and package. As the package diameter increases, the pressure which is exerted in the cylinders is reduced in such a manner that the slide lowers by its own weight. In so doing, stick-slip effects are likewise not preventable. This winding machine is not suitable for a lossfree winding of two alternately operating winding spindles, since it would need for this purpose in addition a rotatable revolver on which the two winding spindles are supported.
It is the object of the present invention to provide a yarn winding apparatus and method of the described type and wherein the radial contact pressure between the contact roll and the package does not unsteadily fluctuate and changes only little in the course of a winding cycle, and which is constructed in a simple and compact manner.